In many manufacturing applications, particularly in food processing, it is highly desirable to interleave the finished articles with thin, flexible sheets of waxed paper, cellophane, plastic film, or other very thin, flexible material. For example, in packaging meat slices or hamburger patties, individual sheets of waxed paper or like material inserted between adjacent pieces of meat prevent the meat from sticking together and preserve the integrity of the individual meat pieces. The same sitution is presented with stacks of sliced cheese; the cheese slices tend to "grow" back together unless the slices are separated by sheets of thin, flexible material.
Often, in the basic processing equipment, there is some stage of operation at which the individual hamburger patties or other such articles traverse a given discharge path, usually terminating at a stacking position; the preferred technique is to suspend individual sheets of waxed paper or the like at some intermediate position on the path so that each article, moving along the path, picks up a sheet of paper and comes to rest in a stack in which the articles are interleaved one-for-one with the paper sheets.
One known interleaving device, comprising an accessory to a hamburger patty machine, is described in Richards et al U.S. Pat. No. 3,126,683, issued Mar. 31, 1964. In the Richards device, the hamburger patties fall freely through space along a predetermined path terminating at a stacking destination. In that device, a sheet of paper is supported at its opposite edges on a frame positioned so that the paper sheet extends across the path of movement of the hamburger patties. A falling hamburger patty engages the sheet of paper and carries the paper with it, through the frame and onto the stack. This device works efficiently in some applications, but does require the use of paper that is wide enough and stiff enough to be self-supporting on frame members that are spaced by a distance greater than the maximum dimension of the hamburger patties. Consequently, the paper must be considerably wider than the patties with which it is interleaved, particularly if thin paper is employed. The apparatus has some tendency toward malfunction, even when relatively wide sheets of paper are used, in that they may occasionally fall from the frame before being engaged by a hamburger patty, resulting in a failure to achieve effective interleaving.
Another prior art interleaving apparatus is set forth in Bush U.S. Pat. No. 2,877,120, issued Mar. 10, 1959, in which individual sheets of paper are cut from a continuous web by a knife mechanism. The paper is held at the cutting position, projecting outwardly from the knife as a cantilever member, and is supported by jet air stream that impinges upon the bottom of the paper. A slice of meat or similar article engages the cantilever-supported paper and carries the paper with it to a stacking location. The jet stream, however, is somewhat difficult to adjust to maintain the paper in the proper position. Moreover, the mechanism is best employed with an apparatus in which the movement of the meat slices or other articles is more closely controlled than in many hamburger patty machines and the like, where there may be some variation in the movement of the objects along the discharge path.
In most interleaving devices using stacks of pre-cut sheets of thin waxed paper or like material, the individual sheets are initially pulled from the stack in a direction including a substantial vector component parallel to the plane of the paper. This produces a tendency toward double-sheeting, particularly if the coefficient of friction between sheets varies, as is often the case. Double-sheeting is highly undesirable; in some applications, it is completely unacceptable. The problem may be alleviated somewhat by using a tear pin with specially punched sheets, but this expedient introduces an almost equally objectionable problem of chaff, from the punched paper, engaging and adhering to the food product. A similar difficulty is experienced with interleavers that stack up two or more sheets at the interleaving position whenever the hamburger patty machine or other food processing equipment with which the interleaver is utilized malfunctions and fails to pass patties through the interleaving position for one or more cycles of operation.
Many of these problems are effectively controlled or minimized by the sheet applying device described in Lekan U.S. Pat. No. 3,675,387, issued July 11, 1972. In that apparatus, an open carriage equipped with two vacuum grippers pulls sheets from a supply hopper and transfers them into the discharge path of the hamburger patties or like articles. As each sheet is pulled onto the carriage it is bent so that cantilever suspension of the sheet becomes possible. This device permits use of smaller sheets than the Richards et al interleaver and is somewhat more consistant in positioning the sheets than the Bush air-jet lift. However, the use of a cantilever suspension is a limiting factor; even with consistent bending of the sheets, erratic operation may occur when extremely flexible sheets are used.